A long-term investigation that involved the rare use of wiretaps by Suffolk County prosecutors led to the seizure of large amounts of deadly fentanyl, the arrests of 33 people, and the breaking up of a ring allegedly with a direct tie to the Sinaloa Mexican drug cartel, officials said.

The drug ring was allegedly led by Edward Soto-Perez of Roxbury, who Suffolk District Attorney Daniel F. Conley said used counter-surveillance techniques so frequently and with such success that Conley decided to get court approval for wiretaps.

“Soto-Perez was clever and extremely diligent in covering his tracks,” Conley said during a news conference Thursday. “He used couriers to make deliveries and take cash payments. He switched cars regularly to foil court-authorized GPS tracking.

And he would make as many as five sudden turns in the span of a mile to spot police surveillance teams.”

The investigation involved the Drug Enforcement Administration as well as Boston, Braintree, and Randolph police, officials said.

A fentanyl kingpin with direct links to Mexico's vicious Sinaloa drug cartel was busted by Boston police and DEA agents before dawn this morning, authorities said.

"Operation High Hopes has taken down one of the Boston area’s top traffickers of fentanyl, heroin, cocaine, and opiate painkillers," Suffolk District Attorney Daniel F. Conley said, referring to a six-month multiagency investigation that resulted in multiple arrests today. "But it did not stop there. It continued up the ladder to identify a second group at the top of the domestic pyramid – one with direct ties to Mexico’s Sinaloa Cartel. The leader of that group, Robert Contreras, age 42 of Dorchester, was taken into custody this morning, along with about a dozen co-conspirators."

Conley said investigators have seized more than 33 pounds of suspected fentanyl – a substance, he noted, that is so deadly it can kill with just a few milligrams.

Authorities also seized about seven and a half kilograms of suspected cocaine, about six kilograms of suspected heroin, and six thousand tablets believed to be opiate painkillers.

The busts were announced by Conley, Boston Police Superintendent in Chief William Gross and Drug Enforcement Administration's New England Division Special Agent in Charge Michael J. Ferguson, and other law enforcement partners today today.

This investigation began in July, when the Boston Police Special Investigations Unit and DEA Task Force Two were probing a trafficking organization run by Edward Soto-Perez, age 43 of Roxbury, Conley said.

"Using cooperating witnesses, controlled purchases, physical surveillance, and other means, they had reliable evidence that he was a kilogram-weight trafficker – but they hit a wall in determining where he stored his supply or who his supplier was," he said. "Soto-Perez was extremely diligent in covering his tracks. He used couriers to make deliveries and take payments. He switched cars to foil court-authorized GPS tracking. And he would make as many as five sudden turns in the span of a mile to spot surveillance teams."

The DA's office took the rare step of approving a wiretap application to get critical evidence about Soto-Perez's suppliers and stash houses, an first application was granted in September after review by a Superior Court judge .

"In the months that followed, the court extended the wiretap 11 times and approved interceptions on more than two dozen phones," Conley said."Investigators doubled as codebreakers to reveal the criminal enterprise as it unfolded. In some calls, the defendants referred to drug shipments as 'musicians' and to payments as 'tickets' to the party. In others, they discussed purity levels by referring to a kilogram of cocaine as a 'car' that could fit 'three passengers' – a highly potent original product that could be quadrupled in retail weight with cutting agents."

The wiretap identified Soto-Perez’ partners and led to search warrants on their stash houses in Dorchester, Conley said.

"But most importantly, it identified his supplier – Contreras," he said.

Prosecutors allege that the Contreras Organization worked with members of the Sinaloa Cartel, one of the most powerful drug trafficking organizations in the world, who imported huge quantities of narcotics into the northeastern United States, Conley said.

"In fact, we believe they were so high in the distribution structure that the next level up would be outside the United States," he said. "Evidence suggests that the Contreras Organization would receive those cartel narcotics and distribute them to the Soto-Perez Group and others, who would in turn supply lower-level dealers."

Over the past six months, drugs were seized in Boston, Brockton, Lynn, Randolph, Wilmington, and as far away as Pennsylvania, Conley said.

Soto-Perez and two co-conspirators – Nelson Catala-Otero, age 37 of Brockton, and Julio Cuello, age 52 of Dorchester – were arrested late last year in the course of the investigation. They are currently held on bails ranging from $100,000 to $250,000 after arraignment in Dorchester court. A fourth man is in custody in Essex County on related charges out of Lynn. All of them will face additional charges, Conley said.